Chronic lymphocytic leukemia (CLL) is the most common leukemia in the United States. CLL involves the cancerous proliferation of lymphocytes. It is most common among older adults; 90 percent of the cases are in people more than 50 years old. It occurs 1-3 times more often among men than among women. The onset of CLL tends to be insidious, with symptoms developing gradually. Because it involves an overproduction of mature, functional lymphocytes, persons with this disorder may survive for years. In contrast, in some, the disorder proceeds very rapidly, and requires immediate treatment. Currently, the adenine deoxynucleosides fludarabine (fludara) and 2-chlorodeoxyadenosine (2CdA) are the drugs of choice to treat the disease. However, clinical remissions are seldom induced, and patients eventually succumb from their leukemia.
The number of nonsteroidal anti-inflammatory drugs (NSAIDs) has increased to the point where they warrant separate classification. In addition to aspirin, the NSAIDs available in the U.S. include meclofenamate sodium, oxyphenbutazone, phenylbutazone, indomethacin, piroxicam, sulindac and tolmetin for the treatment of arthritis; mefenamic acid and zomepirac for analgesia; and ibuprofen, fenoprofen and naproxen for both analgesia and arthritis. Ibuprofen, mefenamic acid and naproxen are used also for the management of dysmenorrhea.
The clinical usefulness of NSAIDs is restricted by a number of adverse effects. Phenylbutazone has been implicated in hepatic necrosis and granulomatous hepatitis; and sulindac, indomethacin, ibuprofen and naproxen with hepatitis and cholestatic hepatitis. Transient increases in serum aminotransferases, especially alanine aminotransferase, have been reported. All of these drugs, including aspirin, inhibit cyclooxygenase, that in turn inhibits synthesis of prostaglandins, which help regulate glomerular filtration and renal sodium and water excretion. Thus, the NSAIDs can cause fluid retention and decrease sodium excretion, followed by hyperkalemia, oliguria and anuria. Moreover, all of these drugs can cause peptic ulceration. See, Remington""s Pharmaceutical Sciences, Mack Pub. Co., Easton, Pa. (18th ed., 1990) at pages 1115-1122.
There is a large amount of literature on the effect of NSAIDs on cancer, particularly colon cancer. For example, see H. A. Weiss et al., Scand J. Gastroent., 31, 137 (1996) (suppl. 220) and Shiff et al., Exp. Cell Res., 222, 179 (1996). More recently, B. Bellosillo et al., Blood, 92, 1406 (1998) reported that aspirin and salicylate reduced the viability of B-cell CLL cells in vitro, but that indomethacin, ketoralac and NS-398, did not.
C. P. Duffy et al., Eur. J. Cancer, 34, 1250 (1998), reported that the cytotoxicity of certain chemotherapeutic drugs was enhanced when they were combined with certain non-steroidal anti-inflammatory agents. The effects observed against human lung cancer cells and human leukemia cells were highly specific and not predictable; i.e., some combinations of NSAID and agent were effective and some were not. The only conclusion drawn was that the effect was not due to the cyclooxygenase inhibitory activity of the NSAID.
The Duffy group filed a PCT application (WO98/18490) on Oct. 24, 1997, directed to a combination of a xe2x80x9csubstrate for MRPxe2x80x9d, which can be an anti-cancer drug, and a NSAID that increases the potency of the anti-cancer drug. NSAIDs recited by the claims are acemetacin, indomethacin, sulindac, sulindac sulfide, sulindac sulfone, tolmetin and zomepirac. Naproxen and piroxicam were reported to be inactive.
Therefore, a continuing need exists for methods to control cancers, such as leukemias, and to increase the potency of anti-cancer drugs with relatively non-toxic agents.
In one aspect, the present invention provides a therapeutic method to treat leukemia, e.g. chronic lymphocytic leukemia, comprising administering to a mammal afflicted with leukemia an amount of etodolac, R(xe2x88x92) etodolac, or an analog thereof, effective to inhibit the viability of leukemic cells of said mammal. The present invention also provides a method of increasing the susceptibility of human leukemia cells, such as chronic lymphocytic leukemia (CLL) cells, to a chemotherapeutic agent comprising contacting the cells with an effective sensitizing amount of etodolac, or an analog thereof. Thus, the invention provides a therapeutic method for the treatment of a human or other mammal afflicted with a leukemia such as CLL, wherein an effective amount of etodolac or an analog thereof is administered to a subject afflicted with leukemia and undergoing treatment with a chemotherapeutic (xe2x80x9cantineoplasticxe2x80x9d) agent.
Preferably, the R(xe2x88x92) isomer of etodolac is administered in conjunction with one or more chemotherapeutic agents effective against CLL such as fludarabine (fludara) or 2-chlorodeoxyadenosine (2CdA). Unexpectedly, the R(xe2x88x92) isomer of etodolac, which exhibits little anti-inflammatory activity, was found to be responsible for the sensitizing activity of racemic etodolac. Therefore, the present invention also provides a method to treat other forms of cancer, such as breast, prostate and colon cancer with RS or the R(xe2x88x92) enantiomer of etodolac or an analog thereof, used alone, or preferably, in combination with a chemotherapeutic agent.
A method of evaluating the ability of etodolac to sensitize leukemia cells, such as CLL cells, to a chemotherapeutic agent is also provided. The assay method comprises (a) isolating a first portion of leukemia cells, such as leukemic B cells, from the blood of a human leukemia patient; (b) measuring their viability; (c) administering etodolac, or an analog thereof, to said patient; (d) isolating a second portion of leukemia cells from said patient; (e) measuring the viability of the second portion of leukemia cells; and (f) comparing the viability measured in step (e) with the viability measured in step (b); wherein reduced viability in step (e) indicates that the cells have been sensitized to said chemotherapeutic agent.
Preferably, steps (b) and (e) are carried out in the presence of the chemotherapeutic agent, as will be the case when the leukemia cells are derived from the blood of a mammal afflicted with leukemia, such as a CLL patient.
Thus, a cancer patient about to undergo, or undergoing, treatment for leukemia can be rapidly evaluated to see if he/she will benefit from concurrent chemotherapy and administration of etodolac or an analog thereof.
The present invention is based on the discovery by the inventors that racemic etodolac inhibits the viability of purified CLL cells at concentrations that do not inhibit the viability of normal peripheral blood lymphocytes (PBLs). It was then unexpectedly found that the R(xe2x88x92) enantiomer of etodolac is as toxic to CLL cells as is the S(+) enantiomer. It was then found that etodolac synergistically interacted with fludarabine and 2-chloroadenosine to kill CLL cells at concentration at which the chemotherapeutic agents alone were inactive.
Etodolac and its analogs possess several unique disposition features due to their stereoselective pharmacokinetics. In plasma, after the administration of RS-etodolac, the concentrations of the xe2x80x9cinactivexe2x80x9d R-enantiomer of etodolac are about 10-fold higher than those of the active S-enantiomer, an observation that is novel among the chiral NSAIDs. See, D. R. Brocks et al., Clin. Pharmacokinet., 26, 259 (1994). After a 200 mg dose in six elderly patients, the maximum plasma concentration of the R-enantiomer was about 33 xcexcM. In contrast, the maximum concentration of the S-enantiomer was 5-fold lower. The typical dosage of the racemic mixture of etodolac is 400 mg BID, and the drug has an elimination half-life between 6-8 hours. Thus, etodolac at commonly used dosages should achieve a plasma concentration of the R-enantiomer shown to sensitize CLL cells in vitro to fludarabine. Moreover, it is likely that the administration of the purified R-enantiomer will not display the side effects associated with cyclooxygenase (COX) inhibitors, such as ulcers and renal insufficiency, and thus could be given at considerably higher dosages. It is believed that etodolac can act both directly and indirectly against cancer cells; i.e., by inhibiting factor(s) that would normally block apoptosis.